Data rate control or rate adaptation is a feature found in a number different wireless technologies or networks in different forms, and often involves changing or updating a transmitted data rate based on some measurement and/or based on a control signal. For example, cdma2000 High Rate Packet Data system is one type of wireless technology and is commonly referred to as 1×DO (“data optimized”) system. The 1×DO system is a single carrier system where Access Terminals (AT) or mobile terminals may communicate with the Access Network (AN) or base station over 1.25 MHz bandwidth in either the forward link (AN-to-AT link) or the reverse link (AT-to-AN link).
In the reverse link of the 1×DO system, there is an access channel mode (including a pilot channel and a data channel) that may be used by an AT to initiate communication with the AN, for example. The reverse link of the 1×DO system also includes a traffic channel mode that may be used by an AT to transmit traffic or signaling information to the AN. The traffic channel mode includes one or two pilot channels, three medium access control (MAC) channels, an acknowledgement (Ack) channel and a data channel. The MAC channels include a reverse rate indicator channel, a data rate control (DRC) channel and a data source control (DSC) channel. In the forward link of the 1×DO system, there is a pilot channel, a medium access control (MAC) channel, an acknowledgement (Ack) channel, a control channel and a traffic channel. The MAC channels include a reverse activity (RA) channel, a DRCLock channel and a reverse power control channel.
In the 1×DO system, the AT measures the signal-to-interference and noise ratio (SINR) during the pilot burst for a number of pilot signals. The AT then uses the measure SINR of the strongest pilot to determine the highest data rate it can reliably decode. The AT then uses the DRC channel (on the reverse link) to inform the AN of the desired data rate on the forward link (AN-to-AT link) and the selected cell sector.
Multi-carrier modulation is a modulation technique where data is modulated onto multiple carriers or subcarriers, rather than being modulated onto a single carrier. Orthogonal Frequency Division Multiplexing (OFDM) is an example of multi-carrier modulation where the subcarriers are orthogonal to each other. Multi-carrier Code Division Multiple Access (MC-CDMA) is another example multi-carrier technology that uses both multiple carrier and spreading codes that may have orthogonal properties. In each frequency band, the transmission technology or format may be similar to or the same as those used in a single carrier system.
Recently, multi-carrier 1×EV-DO (e.g., N×DO) has been proposed for cdma2000 evolution. For example, in a 1×DO variety, the AT and AN would communicate over a 5 MHz radio channel that provides 3 carriers, with a 1.25 MHz frequency band per carrier. An N×DO system is a multi-carrier system that allows ATs to communicate with AN over multiple 1.25 MHz bands—each band may utilize transmission technology and format similar to those used in a 1×DO system. Due to the frequency selective fading and other distortion that may occur independently on each carrier in such a multi-carrier system, it may be useful to allow data rate control information to be communicated between an AT and AN for each carrier.
There is a proposal to time division multiplex (TDM) the DRC values or DRC signals for multiple carriers over the Q (quadrature) branch of the transmitter. Qualcomm, “cdma2000 evolution technology summary,” Presentation in cdma2000 evolution workshop, C00AIE-20050310-027R1, Mar. 10, 2005. In the proposal, the TDM reporting of DRC values uses a long DRC span of 8 slots and DRC length of 2 slots, and 4 DRC values are reported on one reverse link carrier every 13.3 ms. The drawbacks of such proposal include the long DRC span may reduce the forward link channel sensitive schedule gain. The default setting of DRCLength is 4 slots for soft handoff (SHO) region, and the DRC Gain may need to be increased to support a shorter DRCLength, such as a DRCLength of 2 slots. In addition, with all DRC values being reported on the Q-branch, this will typically increase the mobile transmitter's Peak to Average (P/A) ratio.